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Búsquedas previas al 2023, Núm. 3. En la sección Volúmenes 30 - 41 (2012 - 2023).
Molecular aspects of phaseolotoxin biosynthesis produced by Pseudomonas syringae pv. phaseolicola
By Alejandra Chacón López, José Luis Hernández Flores, Efigenia Montalvo González, Selene Aguilera Aguirre*
* Corresponding Author. Email: / Institution:
Received: 20/August/2024 – Published: 30/December/2024 – DOI: https://doi.org/10.18781/R.MEX.FIT.2308-2
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Abstract Background/Objective. Phaseolotoxin is produced by one of the most important and studied phytopathogens in the agricultural area: Pseudomonas syringae pv. phaseolicola. This bacterium causes halo blight, a disease that devastates the bean crop. The success of P. syringae pv. phaseolicola is related to its genetic information, which allows it to synthesize deleterious metabolites for its host, such as phaseolotoxin. This research aimed to analyze the molecular basis of the mechanism of action, immunity, genetics involved in the biosynthesis of phaseolotoxin, molecular diagnostic strategies, and molecular techniques developed in Mexico to manage bean halo blight.
Materials and Methods. The search and analysis of the most relevant scientific information regarding the biosynthesis of phaseolotoxin and the molecular studies of the pathogenicity and virulence factors of P. syringae pv. phaseolicola has contributed to the development of molecular strategies focused on the diagnosis and management of halo blight in beans.
Results. P. syringae pv. phaseolicola produce phaseolotoxin, responsible for forming the chlorotic halo characteristic of halo blight, this toxin is an inhibitor of OCTase, an enzyme that participates in the arginine synthesis pathway in beans. The Pht and Pbo chromosomal regions contain genes involved in the synthesis and immunity of phaseolotoxin, and the expression of these genes is regulated by the GacS/GacA system and temperature. The identification of genes involved in the synthesis of pathogenicity and virulence factors, such as phaseolotoxin, has allowed the development of strategies for diagnosis and management of the disease based on DNA amplification and the use of molecular markers that facilitate the identification of bean cultivars resistant to the pathogen.
Conclusion. Molecular studies have contributed to understanding how the phaseolicola pathovar produces phaseolotoxin. This information has been essential to understanding how bacteria have evolved from non-pathogenic to pathogenic variants. In addition, they provide information that allows the development of new strategies for timely diagnosis and contributes to strategies for managing halo blight.
Keywords: Pathogenicity, Virulence, Phytotoxins, Horizontal Transference, Genetic Regulation
Figure 1. Symptoms produced BY P. syringae pv. phaseolicola ON bean. A Y B, Symptoms ON leaves. C Y D, Symptoms ON pods. Source: Adapted FROM Schwartz, (2008); Harveson, (2009).
Figure 2. Phaseolotoxin structure and PSOrn, product of phaseolotoxin degradation by plant peptidases.
Figure 3. Graphic representation of the Pht and Pbo Regions on P. syringae pv. phaseolicola chromosome. A, Pht Region operons. B, Pbo Region operons. Each arrow represents one gene, the direction of the arrow indicates the direction of transcription.
Figure 4. Model of signaling and regulation of phaseolotoxin biosynthesis in P. syringae pv. phaseolicola NPS3121. Temperature is sensed by the GacS membrane sensor, which autophosphorylates therefore (1). Phosphorylated GacS transfers phosphate to the response regulator GacA (2). GacA controls the expression of pht genes, mediated by the IHF regulator. GacA also controls the transcription of the pbo genes (3). Finally, phaseolotoxin is synthesized, which inhibits bean OCTase and prevents the synthesis of arginine. Consequently, the chlorotic halo develops.
Figure 5. Representative map of the distribution of P. syringae pv. phaseolicola in Mexico. The states marked with yellow color indicate the presence of this bacteria.
Table 1. Function of pht genes involved in phaseolotoxin synthesis.
Table 2. Prediction of the function of pbo genes involved in the phaseolotoxin synthesis.
Table 3. Oligonucleotides used to identify strains of P. syringae pv. phaseolicola producing phaseolotoxin.
